Havnegade & Søborg, Denmark
The Citygreen® modular Stratacell™ system is becoming the main choice of suspended pavement system for tree pits in various urban development projects in Denmark.
Andreas Brunnum, from LK Group, was the project manager for the Havnegade, Kobenhavn (Copenhagen) and the Søborg, Hovedgade projects.
The Havnegade project, which started in September 2011 and finished April 2012, is a one kilometre stretch of urban redevelopment in the harbour area of Copenhagen, where nine trees were planted.
Under the Søborg, Hovedgade project, the Soborg main street was upgraded to become a beautiful greener commercial street. Around 30 trees were planted in the median strip.
The concrete in the media strip was a hindrance for planting trees and getting optimum growth conditions so the old tram rails were removed as well as the thick layer of asphalt and concrete. A total of four sites were renovated around the area.
Brunnum said that by using the Stratacell for the projects, it allowed the trees to grow better. “The pavement will make room for the roots to grow and at the same time you are able to drive the traffic very close to the trees without damaging the roots because of the Stratacells.”
The structural soil cells come in modular units, which can then be assembled to form a skeletal matrix that supports pavement and traffic loads. The Stratacell system features almost five times more available growing media compared to the traditional rock/soil method, therefore facilitating healthy root growth.
As recently proven in a laboratory test in Edmonton, Canada, the Citygreen Stratacell system’s structural integrity can sustain the weight of an ASV PT-50 multi terrain loader. An assembled Stratacell matrix has been FEA tested to 550kPa vertical load. The modules feature extremely high compressive strength and the unique, globally patented, interlocking feature provides correct dispersion of wheel loads throughout the matrix.
It’s the first summer since the trees were planted for the Havnegade project, and although Brunnum says it’s too early to decide whether the system is doing its job, though he is confident it will work.
Brunnum found that after the initial difficulty in figuring out how to use the Stratacells, the next ones were “very easy to use”. “It was not difficult to work with the project.”
“I think we had a very positive feedback from the public. When I visited the area, I could see that many people are using the area for walking and having a talk nearby. I think it was quite a good project for Copenhagen and for the area. This area was not very interesting and not very developed before. I think it has been really good and very useful for Copenhagen,” Brunnum said.
Wyatt Harding, from systems supplier company Milford in Denmark, introduced the Stratacells system in the country a couple of years ago and now supplies most of the big cities in Denmark and around Scandinavia.
He says that although the final results on the health of the trees can’t be determined yet, they have gotten only positive feedbacks about the Stratacells from their clients. The company provides installation support for the initial use of the system and back up support, and finds that clients find it easy to use the system after that. Wyatt says their clients are often quite surprised at how easy it was to put down the Stratacells.
“Because it is a tested product, it’s easy for them to specify,” Wyatt says. Although the rock soil matrix is a cheaper and more common alternative in Scandinavia, Sweden and Denmark, he believes there is quite a big risk involved when a contractor installs it incorrectly.
“We go to the site and we install the first tree pit with them. Any questions they can ask on the site, also we give them tips on how to install more quickly using the numbering and colour coding on the Stratacells. They appreciate that because it’s something in which they feel more at home,” Wyatt adds.
The Citygreen Stratacell’s interconnected skeletal matrix provides over 94 per cent void space for filling with soil media, or storing/detaining storm water. Aside from having a very high strength capacity, the modules are also recyclable and are manufactured from 100 per cent recycled polymer. As there are no steel components, the modules are corrosion free.
“People use it because they don’t want to move cables and pipes and services so they’re optimising the space that’s available with Stratacells because the rock matrix only has about 30 per cent soil volume while the Stratacell has over 90 per cent so you get three times as much soil.”
Although the rock soil matrix is still the most commonly used system in Scandinavia, Stratacells is “becoming more and more popular”.
“Mainly because it’s a safe way of planning and installation. Engineers and architects prefer this. They can now start planning tree pits where they can, also especially because space is a problem in European cities,” Wyatt says.